1. Technical Field
The present disclosure generally relates to the strength training fitness equipment field and, more particularly, to fitness equipment and methods that rely on the user's weight to provide the majority of the resistance during the exercise. The exercise equipment and methods described herein use a closed kinetic chain with resistance exercises which allows the user to perform movements closely associated with normal human function. For user's who are unable to manipulate their own body weight with proper form in this closed kinetic chain the device and methods described herein has the ability to offload body weight, and thus enabling functional exercise to take place.
2. Background Information
The American population is in the midst of a health crisis. The major portion of our society has an overly rich diet and engages in little or—frequently—inappropriate levels and types of exercise. Add the issues of aging over this landscape and it becomes a formula for creating a vast array of medical problems.
There is a vicious cycle to this situation. Being overweight, lacking exercise, and being subject to the wear and tear of aging leads directly to problems with the biomechanical machine that is the human body. Muscles and joints deteriorate, and the effort needed to sustain fitness and appropriate body weight becomes ever more painful and difficult. In turn people stop doing the exact things needed to improve health through exercise.
Even fitness devotees are often subject to these forces. When fitness entered the American consciousness in the 1970s there was little thought given to the formats for exercise. You ran or jumped up and down in classes to create cardiovascular fitness and you lifted free-weights—or used machines that mimic the free-weight movements—to create strength and muscle tone. These approaches served a young demographic quite well, but over time the misuse and even inappropriateness of many of the exercise formats could lead to problems. Many long-term “fit” people are now showing up at orthopedic physicians, chiropractors, and physical therapists with joint and back issues that are a direct result of their former exercise or sports activities.
We as a nation appear to be heading into a period where many of us—particularly those over 60—are sentenced to a life of discomfort and steady decline in our ability to joyfully interact with our physical world.
It does not have to be this way. An approach to living that emphasizes good diet and appropriate exercise can prevent both debilitating disease and injury and even restore an individual's health to where an active and pain-free life is a probable outcome.
Functionally based strength training exercises are those exercises performed in a likeness to how the body works in its normal gravitational environment or how our bodies have evolved to deal with theses gravitational forces. Most functional exercises take place in a closed kinetic chain. A kinetic chain is a motion that is sequential in nature, moving from one segment to the next. One such example occurs when dominos are lined up, stood on end, and one of them falls hitting the next. This sequence continues and the motion is transferred through the entire line of dominos. Closed kinetic chain motion occurs when that same domino attempts to fall forward, but is blocked by an immovable object. An opposing force, created by this immovable object, causes the domino to fall in the opposite direction. The dominos stacked behind the blocked domino begin the motion transfer in the reverse direction. Closed kinetic chain exercise takes place with either the upper extremity or lower extremity fixed on an immovable object. The associated muscles contract in an attempt to move this object. Unable to move the object, the muscle contraction causes motion in the opposite direction, moving the bodies' center of mass instead.
Closed chain motion affects the way our muscles work. Our muscles often function differently in a closed chain than they do in an open chain. This is easily seen in the lower extremity. The hamstring muscle in the back of the thigh bends the knee when contacted in an open chain, but assists in straightening the knee when contracted in a closed chain.
It does not make sense that most exercise machines train our bodies in an open chain. Makers of exercise machines are beginning to realize this and have introduced machines that train the body in a closed kinetic chain. However, for the most part these machines require a significant amount of lower extremity strength to be utilized appropriately and are limited in their closed chain force application to the upper extremity.
Gravity is the force of attraction between two objects. It is a fundamental force of nature that keeps one grounded and must be overcome with every step you make. Our lower extremity musculoskeletal system is designed with large bones and muscles, producing forces that enable us to overcome gravity. The way these muscles work against gravity is slightly different from what we are classically taught. Instead of one muscle flexing a joint and the other extending it, the same muscle is responsible for both actions. The muscles work in conjunction with other muscles in the kinetic chain eccentrically to control the bending caused by gravity and concentrically to overcome it. Since our lower extremities function primarily against closed chain forces, they need to be exercised in a manner that duplicates these forces and therefore improves their functional strength. As we age the maintenance of this closed chain functional strength is a key to preserving our quality of life.
At the other end of the body, the shoulder joint is anatomically unstable in an open chain. Even though we have evolved from using our upper extremities as legs, they are not designed to function solely in an open chain. They are designed to utilize the compressive forces of gravity to assist with joint stabilization. The shoulder has a cuff of musculature (the rotator cuff) to assist in this stabilization. When the compressive forces provided by gravity are utilized in closed chain exercise there is less need for the rotator cuff musculature to stabilize the shoulder joint. On the other hand, motion in an open chain, especially with load, places a great deal of stress on this rotator cuff musculature. Over time the rotator cuff wears out. As a result of this disruption the rotator cuff is a major cause of pain and disability in modern life.
Training the upper extremity musculature in a functional closed chain manner also helps to keep the joints of the upper extremity properly positioned. Most machines and barbell-based forms of exercise require the user to lie or sit on a bench. When this happens the motion of the shoulder blade is limited and even greater stress is placed on the rotator cuff, as the cuff has to stabilize the shoulder joint that is being asked to do too much. The shoulder joint is forced to increase its contribution to the overall motion of the shoulder girdle because the shoulder blade is less able to contribute due to its fixed position. Over time injury to the rotator cuff often occurs.
Lifting the arm overhead in an open chain decreases the need of the eccentric action of the lower rotator cuff and latissimus dorsi to pull the humeral head downward. Without this downward pull, the humeral head rides up in the shoulder joint causing rotator cuff tendon impingement. Closed chain upper extremity exercises—like pull ups in which the arm is moving overhead—utilize this eccentric contraction of the lower cuff and help to prevent impingement.
Training functionally improves strength and, like other forms of resistance training, causes muscle hypertrophy. However, functional training provides superior protection from injury, has a greater metabolic cost due to the multi-joint nature of most of the exercises, and thus tends to be more effective.
The importance of functional training cannot be overstated. Even sports training exercises frequently have little to do with the specific tasks associated with that sport, or do not train all the components of muscular performance. For example, athletes at most levels emphasize strength training in their programs but fail to train their neurological conduction speed. Power is improved by increasing neurological conduction speed. Training that ignores this means athletes are not doing everything they can do to improve their performance.
We need, first and foremost, to be functionally strong. Whether we are athletes, young adults, or retirees, functional training provides benefits to the human machine that are greater than other forms of better known exercise. Most exercise machines available to public apply resistance in an open chain. These machines support the user's weight and allow motion of the distal segment. As such these open chain resistance exercise machines do not provide musculoskeletal adaptation specifically related to how our bodies move in space against gravity.